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Terra
Terra ( ) is the third planet from the Sun, the densest planet in the Sol system, the largest of the Sol system's terrestrial planets, the homeworld of Humans, and the capital of The Conglomerate. Terra is the most populated planet of the human space territories. For a significant amount of humanity's history, it was their only known place in the universe to support life. The combination of Terra's distance from the Sun, its physical properties and its geological history have allowed life to thrive and survive ever close to when the Terra itself formed. Terra's biodiversity has expanded continually except when interrupted by mass extinctions. About 99% of all species of life that have ever lived on Terra are now extinct. Terra's human population is united through The Conglomerate, seperated into further sub-divisions. Chronology Formation By 4.54 Gya the primordial Terra had formed. The formation and evolution of the Solar System bodies occurred along with those of the Sun. The assembly of the primordial Terra proceeded for 10–20 Ma. The process that led to the formation of the Moon approximately 4.53 billion years ago was formed by accretion from material loosed from Terra after a Mars-sized object impacted with Terra. Some of this object merged with Terra, and the rest of it had formed Luna. Themass of Theia was 10% of that of Terra, it impacted Terra with a glancing blow, and some of its mass merged with Terra. Geology Terra's atmosphere and oceans formed by volcanic activity and outgassing that included water vapor. The origin of the world's oceans was condensation augmented by water and ice delivered by asteroids, protoplanets, and comets. Atmospheric greenhouse gases kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Gya, Terra's magnetic field was established, which prevented the atmosphere from being stripped away by the solar wind. A crust formed when the molten outer layer of Terra cooled to form a solid as the accumulated water vapor began to act in the atmosphere. Continents formed by plate tectonics, a process ultimately driven by the continuous loss of heat from Terra's interior. On time scales lasting hundreds of millions of years, the continents have formed supercontinents three times. The present pattern of ice ages began about 40 mya and then intensified about 3 mya. High-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating every 40–100,000 years. The last major continental glaciation ended 10,000 years ago. Composition Structure Terra's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the, and the thickness of the crust varies: averaging 6 km under the oceans and 30–50 km on the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are composed. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core. Heat Terra's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%) from elements such as uranium. Surface Terra's terrain varies greatly from place to place. About 70.8% of the surface is covered by water, with much of the continental shelf below sea level. The planetary surface undergoes reshaping over geological time periods due to tectonics and erosion. The surface features built up or deformed through plate tectonics are subject to steady weathering and erosion from precipitation, thermal cycles, and chemical effects. Glaciation, coastal erosion, the build-up of coral reefs, and large meteorite impacts also act to reshape the landscape. The elevation of the land surface varies from the low point of −418 m at the Dead Sea, to a 2005-estimated maximum altitude of 8,848 m at the top of Mount Everest. The mean height of land above sea level is 840 m. Besides being divided logically into Northern and Southern hemispheres centered on the poles, Terra has been divided arbitrarily into Eastern and Western hemispheres. Dynamics Hydrosphere The natural abundance of liquid, flowing water on Terra's surface is a feature that distinguishes Terra from other planets in the Sol System. The abundance of water on Terra's surface is a unique feature that distinguishes the "Blue Planet" from other planets in the Solar System. Terra's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m. The deepest underwater location is in the Pacific Ocean with a depth of 10.9 kilometers. About 97.5% of the water is saline; the remaining 2.5% is fresh water. Most fresh water, about 68.7%, is present as ice in ice caps and glaciers, frozen. Atmosphere The atmospheric pressure on Terra's surface is about 1 atmosphere, or 101.325 kPa, with a scale height of about 8.5 km. It has a composition of 78% nitrogen and 21% oxygen, 1% argon, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. The outline shine of the atmosphere has a blue tint, matching the color of the water on Terra's surface. Terra's atmosphere is standard of planets, decreasing in density the further away from the surface, giving the atmosphere five main components. *Exosphere: 700 to 10,000 km *Thermosphere: 80 to 700 km *Mesosphere: 50 to 80 km *Stratosphere: 12 to 50 km **Ozone: 15 to 35 km *Troposphere: 0 to 12 km Terra's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 Gya, forming the primarily nitrogen–oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms and, indirectly, the formation of the ozone layer due to the subsequent conversion of atmospheric O2 into O3. The ozone layer blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Water vapor, carbon dioxide, methane and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C, in contrast to the current 15 °C, and life would likely not exist as Terra would literally be a snowball planet. Climate and weather This lowest layer of Terra's atmosphere is called the troposphere. Energy from Sol heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises, and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy. The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°. Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions. The amount of solar energy reaching Earth's surface decreases with increasing latitude. At higher latitudes the sunlight reaches the surface at lower angles and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4 °C (0.7 °F) per degree of latitude from the equator. Earth's surface can be subdivided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical, subtropical, temperate and polar climates. Terra also has several extreme isolated zones, with temperatures ranging from 56.7 °C (134.1 °F) to −89.2 °C (−128.6 °F). Magnetosphere Like all planets, the main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts kinetic energy of fluid convective motion into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth's surface. The magnetic poles is very close to the geographical poles. At the equator of the magnetic field, the magnetic-field strength at the surface is 3.05 × 10−5 Teslas. The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago. Terra's Magnetosphere sufficiently protects the planet from intense solar wind from Sol. In turn, the magnetosphere protects the atmosphere, which itself further protects life on Terra from Ultraviolet radiation. Orbit and rotation Rotation The Earth rotates once in about 24 hours with respect to the sun and once every 23 hours, 56 minutes and 4 seconds with sidereal rotation. Earth's rotation is slowing slightly with time; decreasing 1.7 milliseconds each century on average due to the effects of tidal braking by the Moon. This is accounted for by leap seconds. Category:Terra Category:Planets